Continuous diffusion denuding with moving denuding surface

ABSTRACT

A duct can be configured to receive a denuding gas flow. A solid denuding surface that is connected to a drive system can be configured to move the solid denuding surface within the duct while the solid denuding surface is continuously concentrating one or more gas-phase species from the denuding gas flow on the denuding surface. Also, a denuding gas flow can be passed along a denuding surface to concentrate one or more gas phase species from the denuding gas flow onto the denuding surface with a diffusion denuding action. The denuding surface can be moved while continuing to concentrate the one or more gas phase species from the denuding gas flow onto the denuding surface.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/919,462, filed Oct. 21, 2015, which is a divisional of U.S.application Ser. No. 13/531,457, filed Jun. 22, 2012, which isincorporated herein by reference. If any disclosures are incorporatedherein by reference and such incorporated disclosures conflict in partor whole with the present disclosure, then to the extent of conflict,and/or broader disclosure, and/or broader definition of terms, thepresent disclosure controls. If such incorporated disclosures conflictin part or whole with one another, then to the extent of conflict, thelater-dated disclosure controls.

BACKGROUND

A process by which one or more specific reactive gas phase species(i.e., a pure gas phase species, a vapor phase species, and/or a speciesthat is a combination of gas and vapor phases) are extracted from a gasflow (which may be a pure gas flow or an aerosol that includes suspendedparticles and/or droplets) by bringing the molecules of the gas phasespecies into contact with a reactive denuding surface through diffusionis referred to as diffusion denuding of the gas flow. Diffusion denudingcan take place either passively (without moving the gas flow across thedenuding surface) or actively (by moving the gas flow across thedenuding surface).

SUMMARY

The description herein relates to a moving reactive surface across whichis passed a moving gas flow that is continuously being denuded ofspecific reactive gas phase species contained therein (i.e., thatcontinues to be denuded even while the surface moves). Continuouslymoving a gas flow across a moving solid reactive surface (the denudingsurface) can facilitate continuous concentration and collection oftargeted gas phase reactive species onto the solid denuding surface andmay allow subsequent analysis by one or more of a variety of methods. Inaddition, denuding of these reactive gas phase species from the gas flowcan be used to control and prevent the emission of these gas phasespecies.

According to one embodiment, a duct is configured to receive a denudinggas flow. A solid denuding surface can be connected to a drive system,which can be configured to move the solid denuding surface within theduct while the solid denuding surface is continuously concentrating oneor more gas-phase species from the denuding gas flow on the denudingsurface.

According to another embodiment, a denuding gas flow can be passed alonga denuding surface to concentrate one or more gas phase species from thedenuding gas flow onto the denuding surface with a diffusion denudingaction. The denuding surface can be moved while continuing toconcentrate the one or more gas phase species from the denuding gas flowonto the denuding surface.

This Summary is provided to introduce a selection of concepts in asimplified form. The concepts are further described below in theDetailed Description. This Summary is not intended to identify keyfeatures or essential features of the claimed subject matter, nor is itintended to be used to limit the scope of the claimed subject matter.Similarly, the invention is not limited to implementations that addressthe particular techniques, tools, environments, disadvantages, oradvantages discussed in the Background, the Detailed Description, or theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an analytical apparatus configuredto perform continuous diffusing denuding with a moving denuding surface.

FIG. 2 is a broken away sectional view of an exposure zone of ananalytical apparatus such as the apparatus of FIG. 1.

FIG. 3 is a broken away sectional view of a continuous diffusiondenuding apparatus for controlling emissions.

FIG. 4 is a flowchart of a technique for continuous diffusion denudingwith a moving denuding surface.

The description and drawings may refer to the same or similar featuresin different drawings with the same reference numbers.

DETAILED DESCRIPTION

This description relates to a moving denuding surface that chemicallyreacts with specific reactive gas phase species such as hydrogenchloride (HCl), chlorine (Cl2), sulfur trioxide (SO3), hydrogen sulfide(H2S), etc. in a gas flow that is moving across this reactive surface.Such diffusion denuding can be applicable to pre-concentration of theseand other gas phase species onto a solid surface prior to analysis witha variety of elemental and chemical sensors such as X-ray fluorescence,laser induced ablation spectroscopy, colorimetry, etc. The descriptionbelow will describe one or more methods of extracting and possiblyanalyzing these gas phase species, and one or more apparatuses used toperform the extraction and possibly the subsequent analysis. Althoughthe described techniques and tools can be used for analysis of speciesin a gas flow, they can also be applied in the emission control fieldwhere a continuously refreshed surface can be moving through an emissionaerosol extracting reactive gas phase species.

This arrangement can produce benefits that are not present in orpredictable from prior analysis and removal techniques and tools. Forexample, the tools and techniques described herein may reduce adverseeffects such as fouling of the denuding surface by particulate matter(PM) dust and/or exceeding the denuding surface's reactive capacity.However, the subject matter defined in the appended claims is notnecessarily limited to the benefits described herein. A particularimplementation of the invention may provide all, some, or none of thebenefits described herein. Although operations for the varioustechniques are described herein in a particular, sequential order forthe sake of presentation, it should be understood that this manner ofdescription encompasses rearrangements in the order of operations,unless a particular ordering is required. For example, operationsdescribed sequentially may in some cases be rearranged or performedconcurrently. Techniques described herein with reference to flowchartsmay be used with one or more of the systems described herein and/or withone or more other systems. Moreover, for the sake of simplicity,flowcharts may not show the various ways in which particular techniquescan be used in conjunction with other techniques.

I. Analytical Apparatus

A. Example of the Apparatus

Referring to FIG. 1, an example of an analytical apparatus (100) isillustrated in schematic form. The apparatus can include a flow controlsystem (110) that can provide a gas flow to be analyzed. For example,the flow control system (110) can include a slip stream flow duct (112),which can transport a portion (the slip stream flow (114)) of a flow,such as a portion of a stack gas flow from a stack to a sample inlet(116). For example, the slip stream flow duct (112) may begin at a probelocated within a stack wherein stack gas is flowing. The sample inlet(116) may be a probe located within the slip stream flow (114) in theslip stream flow duct (112).

Referring now to FIGS. 1-2, the sample inlet (116) can lead to a sampleduct (118) that carries a sample flow (120) from the sample inlet (116)and through an exposure zone (124), where the sample flow (120) can flowalong a denuding surface (130). For example, the denuding surface (130)can be a surface of a coating (132) on a substrate such as a tape (134).

The coating (132) can include reactive materials that can react with andtrap one or more gas phase species from the sample flow (120) on thedenuding surface (130) when the molecules of the species contact thedenuding surface (130). The type of the coating (132) can be selectedbased on its ability to trap the one or more species of interest whileexcluding other, potentially interfering species. While it can bebeneficial for the coating (132) to be selective in the species that ittraps, such selective properties need not be perfect. Some sensors, suchas X-ray fluorescence may provide additional selectivity as well asanalyte quantification. As an example, the coating (132) may includeelemental iodine if a species to be denuded is mercury. As anotherexample, Orthotolidine could be used. Also, the same types of coatingsthat have been used in batch denuding applications could be used (e.g.,sodium bicarbonate, sodium hydroxide, some Glycerin could be added,etc.).

The denuding surface (130) could be the surface of a tape or some othertype of solid substrate. For example, the substrate could be a string,etc. The substrate could be made of one or more of various differenttypes of materials, such as Teflon, Mylar, Polycarbonate, biomembranefilter tape such as a coated polyethersulfone filter tape (where theaerosol can be directed across the filter tape instead of through thefilter tape).

As an example, Orthotolidine can be dissolved in acetone, and thesubstrate can be dipped in the resulting solution to form the coating(132). As another example, elemental iodine can be dissolved in Pentane,and the substrate can be dipped in the resulting solution to form thecoating (132).

The tape (134) can be fed from a tape dispensing spool (140), into andalong the exposure zone (124) in the sample duct (118), out of theexposure zone (124), and onto a tape take-up spool (142). A drive systemcan include a controlled-rate motor (144) such as a step motor, whichcan feed the tape (134) from the tape dispensing spool (140) to the tapetake-up spool (142). The sample duct (118) can lead from the exposurezone back to the slip stream flow duct (112), so that the sample flow(120) can flow back to the slip stream flow (114) after diffusiondenuding of one or more species on the denuding surface (130) hasoccurred.

The apparatus (100) can also include a sensor (150), which can be achemical sensor that utilizes one or more sensing techniques such asX-ray fluorescence, laser induced ablation spectroscopy, colorimetry,etc. In the illustrated example in FIG. 1, the sensor (150) is an X-rayfluorescence sensor with an X-ray tube (152) and an X-ray detector(154). The sensor (150) can transmit its sensing results to a dataprocessing and reporting system (160). For example, the data processingand reporting system (160) can include a programmable logic controller,a computer running software, and/or other processing and reportingsystems. The data processing and reporting system (160) may also includeone or more processors, memory, input devices, output devices, buses,connections between such devices, etc. For example, the data processingand reporting system (160) may include a keyboard, mouse, trackball,touch screen, etc. for receiving user input. The data processing andreporting system (160) may also include a computer display fordisplaying results of the data processing, for prompting for user input,etc. The data processing and reporting system (160) can includeinstructions (e.g., code and/or logic circuits) that when executed canprocess data from the sensor (150) and report results of the processingin a manner that allows the sensor (150) to continue collecting datawhile the processing occurs. For example, the sensor (150) may store andperiodically send data to the data processing and reporting system(160). While the data processing and reporting system (160) isprocessing and/or reporting such data, the sensor (150) may continuesensing and collecting data to be sent to the data processing andreporting system (160) in a later transmission. Thus, the sensor (150)may continuously sense the presence of one or more denuded species whilethe denuding surface (130) is moving, allowing the denuding to beperformed continuously as well.

The apparatus (100) can also include a housing (170), which can housethe sample duct (118), the denuding surface (130) in the exposure zone(124), the tape dispensing spool (140), the tape take-up spool (142),and the sensor (150). The housing (170) can be sealed (though it may notbe entirely leak-proof) to decrease leakage along the flow path for thedenuding surface (130) and the sample flow (120). Additionally,pressurized air may be introduced into the housing to help keep thesample flow (120) contained to its flow path, such as in the exposurezone (124).

The housing (170) could contain different components. For example, thesensor (150) could be located at least partially outside the sealedhousing (170). As another example, at least a portion of the dataprocessing and reporting system (160) could be contained in the housing(170). Also, a distinction between the sensor (150) and the dataprocessing and reporting system (160) could be blurred. For example, thesensor (150) can include some processing capability.

B. Quantitative Diffusion Denuding Analysis Examples

A schematic illustration of the exposure zone is shown in FIG. 2, whichidentifies parameters (W, H, and L) that can affect the effectiveness ofdenuding in the apparatus (100). Similar parameters are illustrated inFIG. 3, which will be discussed more below. As noted above, the sampleflow is directed through the sample duct (118) and along the movingdenuding surface (130), which is moving at a rate R. As illustrated, thedenuding surface (130) can be oriented vertically. Accordingly, theparticles can pass through the exposure zone without depositingsignificant amounts of the particles on the moving denuding surface(130) while the gas molecules, which can move at much higher velocitiesthan particles, can react with the denuding surface (130) to form asolid deposit on the denuding surface (130). With enough time, almostall of the target gas phase species molecules will contact and betrapped on the denuding surface (130), thereby being removed from thesample flow (120). By adjusting the flow rate of the sample flow (120),the residence time during which the gas is in contact with the denudingsurface (130) can be adjusted to assure adequate residence time for ahigh removal efficiency.

As is illustrated in FIG. 2, a parameter W is the width of the exposedarea of the denuding surface (130) and of the sample duct (118) in theexposure zone (124). A parameter H is the height of the sample duct(118) in the exposure zone (124), measured normal to the denudingsurface (130) in this example. A parameter L is the length of thedenuding surface (130) exposed to the sample flow (120).

The following table illustrates some parameters, along with some exampleranges, and a specific example value for each parameter. The parameterswill also be discussed below, following the table. It should beunderstood that the invention is not limited to these example values orranges unless so stated in the claims.

Parameter Symbol & Description Example Range Example Value A_(f) = Gasflow, cross sectional <0.1 cm to 10 cm 0.1 cm × 2 cm = 0.2 cm² area (H ×W) A_(t) = Exposed tape area (L × 1 to 100 cm² 2 cm × 5 cm = 10 cm² W) C= Concentration of analyte PPTV (parts per trillion by 1 to 30 PPMV ingas volume) to PPMV (parts per million by volume) D = Aerial density ofng/cm² to mg/cm² 10 μg/cm² analyte on tape D 

 = Aerial density 0.01 to 10 ng/cm² 1 ng/cm² detection limit D_(m) =Maximum aerial 1-100 μg/cm² 20 μg/cm² density (capacity) F = Samplingflow of stack 0.01-10 lpm 0.1 lpm gas H = Height of opening for 0.01-1cm 0.1 cm gas flow L = Length of tape 1-30 cm 5 cm exposed to gas R =Rate of tape use 0.001-0.01 cm/sec 0.008 cm/sec T_(e) = Gas exposuretime 0.001-0.1 sec >0.1 sec (target) T_(t) = Tape travel time (L/R)100-1000 sec 500 sec V_(e) = Velocity of gas 1-1,000 cm/sec 10 cm/sec(F/A_(f)) V_(o) = Volume of gas 0.01-1,000 liters 1 liter denuded W =Width of exposed .02-20 cm 2 cm area of tape

Following are some examples of parameters for analyzing HCl in emissionsfrom Portland cement plants, coal-fired power plants, incinerators, andindustrial boilers. In these examples, the “Limit” is an example of aregulatory limit for concentration of HCl in emissions, “Capacity” isthe HCl concentration capacity that could be sampled by the reactivedenuding surface, “Design Concentration” is the HCl concentration forwhich the apparatus is designed, and limits of detection (“LOD”) are thelower HCl concentration limits that can be detected with the apparatus.

-   1. Portland Cement Plant and Coal Fired Power Plant    -   a. Limit ˜3 PPMV (5 mg/m³)    -   b. Capacity ≥20 mg/m³    -   c. Design Conc. ˜1 PPMV (˜2 mg/m³)    -   d. LOD ≤0.1 PPMV-   2. Incinerators & Industrial Boilers    -   a. Limits ˜30 PPMV (50 mg/m³)    -   b. Capacity ≥200 mg/m³    -   c. Design Conc. ˜10 PPMV (˜20 mg/m³)    -   d. LOD ≤1 PPMV-   3. Examples for New Regulations    -   a. Limits ≤0.1 PPMV (˜0.2 mg/m³)    -   b. Capacity ≥0.8 mg/m³    -   c. Design Con. ˜0.05 PPMV (˜0.08 mg/m³)    -   d. LOD ≤0.01 PPM

With these parameters in mind, along with the following specific exampletarget design parameters, the equation relating the aerosolconcentration of the species to the measured concentration of thespecies on the moving denuding surface (130) can be derived as indicatedbelow. Target design parameters: W=2 cm; L=5 cm; A_(t)=10 cm²; H=0.1 cm;A_(f)=0.2 cm²; R=0.008 cm/sec; F=0.1 lpm; V_(e)=8.3 cm/sec.

The exposure time (T_(e)) available to denude the gas sample can becalculated according to the following equation.

$T_{e} = {\frac{L}{V_{e}} = {\frac{5\mspace{14mu}{cm}}{8.3\mspace{14mu}{cm}\text{/}\sec} = {0.60\mspace{14mu}{\sec@0.1}\mspace{20mu}{l{pm}}}}}$

The time for the tape to move the 5 cm of exposure length (T_(t)=tapetravel time) can be calculated according to the following equation.

$T_{t} = {\frac{L}{R} = {\frac{5\mspace{14mu}{cm}}{0.008\mspace{14mu}{cm}\text{/}\sec} = {625\mspace{14mu}\sec}}}$

The volume of gas (V_(o)) exposed to the tape in 625 seconds can becalculated according to the following equation.V _(o) =FT _(t)=(100 cc/min)(10.4 min)=1,040 cm³

The analyte aerial density (the density D of the species on the denudingsurface) can be calculated according to the following equation:

$D = {\frac{V_{o}C}{A_{t}} = {{{\lbrack {( {1.038\mspace{14mu} l} )( {1\mspace{14mu}{{mg}/m^{3}}} )} \rbrack/10}\mspace{14mu}{cm}^{2}} = {100\mspace{14mu}{ng}\text{/}{cm}^{2}}}}$$\begin{matrix}{D = {( {{FL}/{RA}_{t}} )C}} & {< {D_{m}\text{∼}20\mspace{14mu}{ug}\text{/}{cm}^{2}}}\end{matrix}$

The following equation can be obtained by solving the above equation forthe analyte gas concentration (C).

$C = {{\frac{{RA}_{t}}{FL}D} = {{\lbrack {( \frac{R}{F} )( \frac{A_{t}}{L} )} \rbrack D} = {KD}}}$

In this equation,

$( \frac{R}{F} )$is a controlled constant that can be controlled by controlling the flowrate of the sample flow (120) and the rate of the moving denudingsurface (130). The term

$( \frac{A_{t}}{L} )$is a design constant that depends on the geometry of the apparatus(100). These two terms

$( {( \frac{R}{F} )\mspace{14mu}{and}\mspace{14mu}( \frac{A_{t}}{L} )} )$can be multiplied together to form a constant K, which can be used toconvert the density D to the concentration C of the species in theaerosol. This equation assumes 100% denuding efficiency. If the denudingefficiency is less than 100% by a significant value, a factor can beintroduced into the conversion equation above to correct for such aninefficiency.

While an example apparatus (100) and example calculations for such anapparatus have been discussed above, changes may be made within thescope of the disclosure herein. For example, different configurations,materials, etc. may be used for the apparatus and for techniques forusing the apparatus.

II. Continuous Diffusion Denuding Apparatus for Controlling Emissions

Referring now to FIG. 3, an example of continuous diffusion denuding forcontrolling emissions will be discussed. FIG. 3 illustrates an exampleof an emission control apparatus (300). The apparatus (300) can includea flow duct (310) surrounding a series of denuding surfaces (320) formedby a flexible sheet (330) wound over and under a series of top rollers(336) and bottom rollers (338) to form a serpentine pattern. Thedenuding surfaces (320) can be positioned parallel to the direction ofmovement of a gas flow (344) that includes one or more species to becontrolled. A drive system (350) can engage the flexible sheet (330) tomove the sheet while one or more gas phase species are beingconcentrated on the denuding surfaces (320) of the flexible sheet (330).For example, the drive system (350) can include a drive motor.

The apparatus (300) can also include a treatment zone (340), which canrefresh the reactive properties of the denuding surfaces (320) as theypass through the treatment zone. For example, the treatment zone (340)could subject the surfaces (320) to chemical solutions, heat, radiation,etc. The refreshing of the surfaces (320) could include regeneratingsurface activity and/or recovering and controlling the one or more gasphase species being controlled.

The apparatus (300) could include different design features. Forexample, the flow could split and go through several such apparatuses inparallel. As another example, several such apparatuses could be arrangedin series in the flow. Also, different configurations for moving thedenuding surfaces (320) could be used. For example, the apparatus couldinclude several separate flexible sheets instead of a single sheet.Also, the denuding surfaces (320) could move in some other manner, suchas in an oscillating motion where parts of the denuding surfaces couldmove into and out of the flow path and the treatment zone as theyoscillate back and forth.

III. Techniques for Continuous Diffusion Denuding with Moving DenudingSurface

Referring now to FIG. 4, a technique for continuous diffusion denudingwith a moving denuding surface will be discussed. The technique caninclude passing (410) a denuding gas flow along a denuding surface toconcentrate one or more gas phase species from the denuding gas flowonto the denuding surface with a diffusion denuding action. Thetechnique can also include moving (420) the denuding surface whilecontinuing to concentrate the one or more gas phase species from thedenuding gas flow onto the denuding surface. This moving could include aseries of movements, as with a stepping motor that drives the denudingsurface while gas is being concentrated on the denuding surface, orcontinuous movement, as with a continuously moving drive motor thatdrives the denuding surface. In either case, the denuding surface ismoved without ceasing the denuding action, as would happen if thedenuding surface were being entirely removed, leaving no denudingsurface in place for some time, as in some batch denuding processes.

The one or more gas phase species could include a species selected froma group consisting of mercury, hydrochloric acid, and combinationsthereof. The denuding surface can include a continuous surface, and thetechnique can include refreshing one or more denuding properties of thesolid denuding surface while concentrating the one or more gas phasespecies from the gas flow onto the denuding surface.

The technique may further include sensing (430) and quantifying (440)quantities of at least one of the one or more gas-phase species. Forexample, the sensing (430) and quantifying (440) may be done with one ormore of the types of sensors and data processing and reporting systemsdiscussed above. The quantifying (440) may quantify the gas-phasespecies such as in terms of density on the denuding surface. Thetechnique may further include receiving (450) data resulting from thesensing (430) and quantifying (440), processing (460), and reporting(470) results of the processing. For example, the processing (460) mayinclude converting density values to concentration values, storing thedensity and/or concentration values, and representing the values intables, graphs, etc. Reporting (470) may include displaying and/ortransmitting representations of the data, such as in the form of suchtables, graphs, etc. However, sensing (430), quantifying (440),receiving (450), processing (460), and/or reporting (470) may beomitted, such as if the technique is for emission control and not foranalysis of species in emissions.

The denuding surface may be a surface of a flexible sheet, or some othersurface such as the surface of a string, etc. The denuding surface canbe oriented vertically while concentrating the one or more gas phasespecies from the gas flow onto the denuding surface. The denuding gasflow can be a portion of a main gas flow, such as a gas flow that hasbeen redirected from the main gas flow. The denuding gas flow can be aportion of a slip gas flow that is a portion of the main flow, with theslip gas flow having been redirected from the main gas flow and thedenuding gas flow having been redirected from the slip gas flow.

The denuding surface may be a surface of a reactive coating on asubstrate, such as coating on a tape.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

I claim:
 1. A denuding apparatus comprising: an exposure zone configuredto receive a denuding gas; a solid denuding surface positioned at leastpartially within the exposure zone and configured to concentrate agas-phase species from the denuding gas on the denuding surface; a drivesystem connected to the solid denuding surface, the drive system beingconfigured to move the solid denuding surface relative to the exposurezone while the solid denuding surface is concentrating the gas-phasespecies from the denuding gas on the denuding surface; and a sensorconfigured to sense quantities of the gas-phase species concentrated onthe denuding surface while the drive system moves the solid denudingsurface relative to the exposure zone and while the solid denudingsurface is concentrating the gas-phase species from the denuding gas onthe denuding surface.
 2. The apparatus of claim 1, wherein the denudingsurface comprises a continuous surface and the apparatus furthercomprises a treatment zone through which the solid denuding surface isconfigured to pass to refresh one or more denuding properties of thesolid denuding surface.
 3. The apparatus of claim 1, wherein the sensoris further configured to quantify quantities of the gas-phase species.4. The apparatus of claim 3, further comprising a data processing andreporting system that is configured to receive data from the sensor,process the data, and reports results of the processing.
 5. Theapparatus of claim 1, wherein the denuding surface is a surface of aflexible sheet.
 6. The apparatus of claim 1, wherein the denudingsurface is oriented vertically while sampling the gas phase species. 7.The apparatus of claim 1, wherein the apparatus further comprises a slipstream flow duct leading from a main gas flow, the slip stream flow ductcarrying a slip stream flow from which the denuding gas is received. 8.The apparatus of claim 1, wherein the denuding surface is a surface of areactive coating on a substrate.
 9. A denuding apparatus comprising: anexposure zone configured to receive a denuding gas; a solid denudingsurface positioned at least partially within the exposure zone andconfigured to concentrate a gas-phase species from the denuding gas onthe denuding surface; a drive system connected to the solid denudingsurface, the drive system being configured to move the solid denudingsurface relative to the exposure zone while the solid denuding surfaceis concentrating the gas-phase species from the denuding gas on thedenuding surface; and a sensor configured to sense quantities of thegas-phase species concentrated on a first portion of the denudingsurface located outside the exposure zone while the drive system movesthe solid denuding surface relative to the exposure zone and while thesolid denuding surface is concentrating the gas-phase species from thedenuding gas on a second portion of the denuding surface that ispositioned within the exposure zone.
 10. The apparatus of claim 9,wherein the sensor is further configured to quantify quantities of thegas-phase species.
 11. The apparatus of claim 10, further comprising adata processing and reporting system that is configured to receive datafrom the sensor, process the data, and report results of the processing.12. The apparatus of claim 9, wherein the denuding surface is a surfaceof a flexible sheet.
 13. The apparatus of claim 9, wherein the apparatusfurther comprises a slip stream flow duct leading from a main gas flow,the slip stream flow duct carrying a slip stream flow from which thedenuding gas is received.
 14. The apparatus of claim 9, wherein thedenuding surface is a surface of a reactive coating on a substrate. 15.A denuding apparatus comprising: an exposure zone configured to receivea denuding gas; a solid denuding surface positioned at least partiallywithin the exposure zone and configured to concentrate a gas-phasespecies from the denuding gas on the denuding surface, the soliddenuding surface being a surface of a reactive coating on a flexiblesheet; a drive system connected to the solid denuding surface, the drivesystem being configured to move the solid denuding surface relative tothe exposure zone while the solid denuding surface is concentrating thegas-phase species from the denuding gas on the denuding surface; and asensor configured to sense quantities of the gas-phase speciesconcentrated on a first portion of the denuding surface located outsidethe exposure zone while the drive system moves the solid denudingsurface relative to the exposure zone and while the solid denudingsurface is concentrating the gas-phase species from the denuding gas ona second portion of the denuding surface that is positioned within theexposure zone.
 16. The apparatus of claim 15, wherein the sheet is atape.
 17. The apparatus of claim 15, wherein the sensor is furtherconfigured to quantify quantities of the gas-phase species.
 18. Theapparatus of claim 17, further comprising a data processing andreporting system that is configured to receive data from the sensor,process the data, and report results of the processing.
 19. Theapparatus of claim 1, wherein the sensor comprises an X-ray fluorescencesensor.
 20. The apparatus of claim 1, wherein the apparatus comprises atape dispensing spool and a take-up spool, and wherein the soliddenuding surface is the surface on a tape that extends from the tapedispensing spool to the take-up spool.
 21. The apparatus of claim 20,wherein the apparatus is configured to pass the tape from the tapedispensing spool, then through the exposure zone, and then to thetake-up spool, and wherein the sensor is configured to sense quantitiesof the gas-phase species concentrated on the denuding surface on thetape between the exposure zone and the take-up spool.
 22. The apparatusof claim 1, wherein the gas-phase species comprises mercury.
 23. Theapparatus of claim 1, wherein: the sensor comprises an X-rayfluorescence sensor; the apparatus comprises a tape dispensing spool anda take-up spool; the solid denuding surface is the surface of a coatingof a tape that extends from the tape dispensing spool to the take-upspool; the apparatus is configured to pass the tape from the tapedispensing spool, then through the exposure zone, and then to thetake-up spool; the sensor is configured to sense quantities of thegas-phase species concentrated on the denuding surface of the coating ofthe tape between the exposure zone and the take-up spool; and thegas-phase species comprises mercury.